In general, methods for treating the surface of a substrate, including removal of contaminants (e.g. organic substances) from the surface of the substrate, removal of resist, attachment of organic film, surface deformation, improved film formation, reduction of a metal oxide, and cleaning of a glass substrate for liquid crystals, are classified into wet cleaning methods using chemicals and dry cleaning methods using plasma.
Conventional wet cleaning methods using liquid chemicals have the advantages of easy processing and inexpensiveness, but have trouble in cleaning micro circuits. In addition, the use of chemicals is not environmentally-friendly.
This necessitates dry cleaning equipment using plasma, which can clean micro circuits, although the technical implementation is not easy.
Plasma mass production technology based on electric arcs at the atmospheric pressure can process a large amount of substances chemically or biologically in actual conditions, and is expected to play a pivotal role in future industries (e.g. materials, energy field, etc.) besides environmental pollution prevention and purification fields.
Low-temperature plasma generation technology is used for various purposes, including dry etching that uses plasma-activated particles, CVD (Chemical Vapor Deposition) for forming a thin film in the semiconductor field, cleaning of thin film deposition chambers for semiconductors using PFC gas, surface modification of solid substances using activated ions or electrons, and sputtering for deposition or coating of a target substrate by accelerating ions, for example, by means of the electric field so that they are incident on the target substance.
An exemplary method for surface treatment using plasma makes use of plasma in a low-temperature and low-pressure state. According to this method, plasma is generated inside a vacuum chamber of low temperature and pressure so that the plasma contacts the surface of a substrate and treats its surface. Despite excellent cleaning performance, this type of method is not widely used because the fact that a vacuum device is needed to maintain low pressure makes its application to continuous processes difficult.
There is also commercialized technology relying on atmospheric electric arcs, such as DC arc-torch. This DC arc type method is characterized in that the arc gas has a temperature of thousands of degrees, and these high-temperature characteristics are currently used to cut or weld metal. There is another type of method utilizing the radio-frequency resonance at the atmospheric pressure to cause an electric arc. The temperature of arc gas during the resulting glow or corona arc is substantially lower than that of other methods using atmospheric arcs.
Such atmospheric low-temperature plasma is used for in-line surface treatment, including cleaning and oxide deposition. If a trace of active gas is added to inactive gas, the resulting arc gas creates a large amount of active particles (e.g. ozone, radicals). The room-temperature characteristics of plasma do not cause thermal deformation of the object, and enable not only treatment of metal, but also treatment of other materials, including plastic and glass.
The atmospheric low-temperature plasma can also make a large contribution to substrate disinfection and PCB cleaning during semiconductor processes. The activity of plasma can be used for in-line treatment of organic metal byproducts of semi-conductor substrates and PCBs. The low-temperature characteristics of plasma make it possible to introduce environmentally-friendly processes that can improve product quality without causing thermal deformation of the object.
Particularly, application of a high voltage to both electrodes, which are spaced from each other, creates an electric arc in the space between them and ionizes the reaction gas. A large number of various functional ions created in this manner collide with the surface of the treated material to clean its surface and remove small alien substances.
Plasma cleaning devices using such atmospheric low-temperature plasma according to the prior art emit plasma via a number of emission nozzles to clean the substrate. In order to confirm whether plasma is emitted or not, photodiodes must be installed on the plasma emission nozzles.
However, this type of plasma monitoring based on photodiodes has a problem in that it can only determine whether plasma is being emitted or not. In other words, this approach cannot measure the amount of emitted plasma throughout the entire area. As a result, the substrate may not be cleaned evenly if plasma is supplied irregularly.